Allow tsc to be run within a node v8 snapshot

.gitignore

@@ -63,3 +63,4 @@ package-lock.json
 .eslintcache
 *v8.log
 /lib/
+*.blob

src/compiler/core.ts

@@ -2744,6 +2744,5 @@ export function isNodeLikeSystem(): boolean {
     // and definitely exist.
     return typeof process !== "undefined"
         && !!process.nextTick
-        && !(process as any).browser
-        && typeof module === "object";
+        && !(process as any).browser; // TODO(jakebailey): figure out a better "is node" check
 }

src/compiler/sys.ts

@@ -1454,8 +1454,8 @@ interface DirectoryWatcher extends FileWatcher {
     referenceCount: number;
 }
 
-// TODO: GH#18217 this is used as if it's certainly defined in many places.
-export let sys: System = (() => {
+/** @internal */
+export function createSystem(): System {
     // NodeJS detects "\uFEFF" at the start of the string and *replaces* it with the actual
     // byte order mark from the specified encoding. Using any other byte order mark does
     // not actually work.
@@ -2008,21 +2008,26 @@ export let sys: System = (() => {
         patchWriteFileEnsuringDirectory(sys);
     }
     return sys!;
-})();
+}
+
+// TODO: GH#18217 this is used as if it's certainly defined in many places.
+export let sys: System;
 
 /** @internal */
 export function setSys(s: System) {
     sys = s;
-}
 
-if (sys && sys.getEnvironmentVariable) {
-    setCustomPollingValues(sys);
-    Debug.setAssertionLevel(
-        /^development$/i.test(sys.getEnvironmentVariable("NODE_ENV"))
-            ? AssertionLevel.Normal
-            : AssertionLevel.None,
-    );
-}
-if (sys && sys.debugMode) {
-    Debug.isDebugging = true;
+    if (sys && sys.getEnvironmentVariable) {
+        setCustomPollingValues(sys);
+        Debug.setAssertionLevel(
+            /^development$/i.test(sys.getEnvironmentVariable("NODE_ENV"))
+                ? AssertionLevel.Normal
+                : AssertionLevel.None,
+        );
+    }
+    if (sys && sys.debugMode) {
+        Debug.isDebugging = true;
+    }
 }
+
+setSys(createSystem());

src/tsc/tsc.ts

@@ -9,16 +9,39 @@ ts.Debug.loggingHost = {
     },
 };
 
-if (ts.Debug.isDebugging) {
-    ts.Debug.enableDebugInfo();
+let v8: typeof import("v8") | undefined;
+try {
+    v8 = require("v8");
 }
-
-if (ts.sys.tryEnableSourceMapsForHost && /^development$/i.test(ts.sys.getEnvironmentVariable("NODE_ENV"))) {
-    ts.sys.tryEnableSourceMapsForHost();
+catch {
+    // do nothing
 }
 
-if (ts.sys.setBlocking) {
-    ts.sys.setBlocking();
+function main() {
+    if (ts.Debug.isDebugging) {
+        ts.Debug.enableDebugInfo();
+    }
+
+    if (ts.sys.tryEnableSourceMapsForHost && /^development$/i.test(ts.sys.getEnvironmentVariable("NODE_ENV"))) {
+        ts.sys.tryEnableSourceMapsForHost();
+    }
+
+    if (ts.sys.setBlocking) {
+        ts.sys.setBlocking();
+    }
+
+    ts.executeCommandLine(ts.sys, ts.noop, ts.sys.args);
 }
 
-ts.executeCommandLine(ts.sys, ts.noop, ts.sys.args);
+if ((v8 as any)?.startupSnapshot.isBuildingSnapshot()) {
+    (v8 as any).startupSnapshot.setDeserializeMainFunction(() => {
+        // When we're executed as a snapshot, argv won't contain the js file anymore.
+        // TODO(jakebailey): if we need to fork TS, we probably need to know the snapshot name and exec that...
+        process.argv.splice(1, 0, __filename);
+        ts.setSys(ts.createSystem());
+        main();
+    });
+}
+else {
+    main();
+}

src/tsc/tsconfig.json

@@ -1,6 +1,7 @@
 {
     "extends": "../tsconfig-base",
     "compilerOptions": {
+        "types": ["node"]
     },
     "references": [
         { "path": "../compiler" },